1. Field of the invention
The present invention relates to a backside light emitting chip type light emitting element to be incorporated in various kinds of thin type machinery and tools.
2. Description of Related Art
FIG. 7 is a schematic sectional view of a conventional backside light emitting chip type light emitting element, and FIG. 8 is a schematic plan view of the same. A pair of internal electrodes 52r, 52l are formed in the inner region on one principal surface of a rectangular insulating substrate 51. A light emitting chip 54 is die-bonded on one internal electrode 52r. The light emitting chip 54 and the other internal electrode 52l are electrically connected to each other by a bonding wire 55. On the principal surface of the insulating substrate 51, a region including the light emitting chip 54, the bonding wire 55, and the connecting portion of the bonding wire 55 on the internal electrode 52l is protected by a light-permeable member 56.
External electrodes 53r, 53l are formed on the opposed end side sections of the insulating substrate 51 so as to extend from the principal surface of the insulating substrate 51 over the side faces thereof, respectively. The internal electrodes 52r, 52l are connected to the external electrodes 53r, 53l in the vicinity of the end sections of the insulating substrate 51, respectively.
Electrode pads 58 are formed at predetermined positions on a wiring substrate 57 on which the above-mentioned backside light emitting chip type light emitting element is mounted. The electrode pads 58 and the external electrodes 53r, 53l of the backside light emitting chip type light emitting element are bonded to one another by solders 59. Since the external electrodes 53r, 53l are formed over the two surfaces, i.e. the above-mentioned surface and the side face of the insulating substrate 51, the light emitting element is supported by the solders 59 at the upper surface and the side faces thereof.
A through hole 60 is provided in the wiring substrate 57, and the backside light emitting chip type light emitting element is supported in such a manner that the light-permeable member 56 section thereof is inserted into the through hole 60. Accordingly, light emitted by the backside light emitting chip type light emitting element is visible in the direction of an arrow A shown in FIG. 7, i.e. from the opposite side of the mounting surface 57a of the wiring substrate 57.
In such a conventional backside light emitting chip type light emitting element as mentioned above, only one light emitting chip 54 is mounted. Therefore, only one kind of emitted light having a fixed color and brightness can be obtained.
On the other hand, when a plurality of insulating substrates 51 are manufactured at a time, individual pieces of insulating substrates 51 are cut out of a large original insulating substrate as shown in FIG. 9. In the original substrate, individual regions 51A (one individual region 51A is shown with hatching in FIG. 9) corresponding to individual pieces of insulating substrates 51 are disposed laterally in close contact with one another and longitudinally in arrangement with slit-shaped spaces B therebetween. The plurality of individual regions 51A constitute a large sheet of substrate supported by a frame section 51B.
The spaces B are required for forming external electrodes 53 by plating or the like on the side faces 51a of the insulating substrates 51. It is also a disadvantage of such a conventional art that, because of providing the spaces B, only a decreased number of individual pieces of insulating substrates 51 can be cut out from a large original insulating substrate.
An object of the present invention is to provide a backside light emitting chip type light emitting element capable of emitting light of two or more kinds of colors, and an insulating substrate used therefor.
Another object of the present invention is to provide a backside light emitting chip type light emitting element having an electrode arrangement capable of obtaining a stable bonding strength when it is mounted on a wiring substrate, and an insulating substrate used therefor.
A backside light emitting chip type light emitting element according to the present invention includes an insulating substrate, at least three internal electrodes formed on one principal surface of the insulating substrate, at least three external electrodes formed on the one principal surface of the insulating substrate and electrically connected to the at least three internal electrodes, and at least two light emitting chips electrically connected to the internal electrodes.
With this structure, by mounting at least two light emitting chips, light of two or more kinds of colors can be emitted. For example, by using light emitting chips having different emission colors respectively and selectively causing one or more of the light emitting chips to emit light, light of two or more colors can be observed. Further, by using a plurality of light emitting chips having the same emission color and changing the number of the light emitting chips emitting light at the same time, the brightness of the emitted light can be changed.
The insulating substrate may be formed substantially rectangular. In this case, the external electrodes can be formed at the corner portions, or a part or the whole of the side sections of the insulating substrate.
In an embodiment of the present invention, the insulating substrate is substantially rectangular, and the external electrodes are formed at at least three corner portions of the insulating substrate, respectively. By forming the external electrodes at the corner portions of the substantially rectangular insulating substrate, the insulating substrate can be strongly bonded to electrode pads provided on a wiring substrate.
Further, in an embodiment of the present invention, one-fourth through holes each having electrically conductive inner wall are formed at the at least three corner portions of the insulating substrate, respectively. Thereby, when the insulating substrate is bonded to a wiring substrate, the insulating substrate is supported also from the side face, so that the bonding strength can become stable. Preferably, the inner wall of each one-fourth through hole is provided with conductivity by the use of a metal material having a favorable solder wetting property.
When manufacturing a backside light emitting chip type light emitting element of the present invention, in the step of cutting out a plurality of individual pieces of insulating substrates each usable for the light emitting element from a larger insulating substrate, through holes are formed in the larger insulating substrate and the inner walls of the through holes are treated so as to become conductive. Then, by cutting the plurality of insulating substrates out of the larger insulating substrate in such a manner that each through hole can be divided into quarters, one-fourth through holes can be formed. By utilizing this, individual regions corresponding to the individual pieces of insulating substrates to be cut out can be disposed in close contact with one another in a larger insulating substrate. As a result, the number of the insulating substrates obtainable from a larger insulating substrate having a predetermined area can be increased.
An inventive insulating substrate used for a backside light emitting chip type light emitting element is formed with at least three internal electrodes and at least three external electrodes connected to the internal electrodes on one principal surface thereof. The external electrodes are disposed on the peripheral part side of the insulating substrate with respect to the internal electrodes.
Such an insulating substrate is usable for the above-mentioned backside light emitting chip type light emitting element.
The insulating substrate used for the backside light emitting chip type light emitting element may be formed to be substantially rectangular. In this case, it is preferable that the external electrodes are formed at at least three corner portions of the insulating substrate, respectively.